Body implantable electrical leads form the electrical connection between stimulation devices, such as a cardiac pacemaker, and target body tissue, such as that of the heart, which is to be electrically stimulated. As is well known, the leads connecting pacemakers with the heart may be used for pacing or for sensing electrical signals produced by the heart, or for both pacing and sensing in which case a single electrical lead serves as a bi-directional pulse transmission link between the pacemaker and the heart. An endocardial electrical lead which is inserted into a vein and guided therethrough into a cavity or chamber of the heart, includes at its distal tip an electrode designed to contact the endocardium. Such an electrical lead further includes a proximal end carrying an electrical connector assembly adapted to be received by a receptacle in the pacemaker. A flexible cable or coil conductor surrounded by an insulating sheath couples a terminal contact on the electrical connector assembly with the electrode at the distal tip.
To prevent displacement or dislodgment of the tip electrode and to maintain the necessary stable electrical contact between the tip electrode and the endocardial tissue, the electrode must be firmly anchored relative to the tissue. To achieve this, one type of lead, sometimes referred to as an active fixation lead, includes a pointed, extendable/retractable helix adapted to be screwed into the heart tissue to be stimulated. In this fashion, the position of the tip electrode is mechanically stabilized by positively anchoring the lead tip so that it remains securely in place during the lifetime of the implant.
The fixation helix may itself comprise the tip electrode in which case it is electrically coupled by means of a coil conductor to a rotatable terminal contact pin on the connector assembly. Rotational torque applied to the connector pin at the proximal end of the lead is transmitted via the coil conductor to the helix electrode which is thereby screwed into the heart tissue. Removal of the screw-in electrode from the endocardium is effected by counter-rotation of the connector pin. Thus, in electrical leads having a screw-in helix electrode, the coil conductor is used not only as a conductor for electrically coupling the connector pin and the helix electrode, but also as a tool for extending or retracting the helix electrode relative to the distal end of the lead during lead fixation or removal by rotating the connector pin.
Such conventional electrical leads are an important element of implantable cardiac stimulation devices and the like. Current electrical lead designs are adequate in many respects, however, they can be difficult to remove and often do not provide sufficient surface area contact of the electrodes. In particular, the area of tissue engaged by a helix electrode is limited by the outer diameter of the lead header. In addition, the helix electrode is limited to a single point of tissue contact for electrical stimulation. What has been needed are electrical leads for electrical stimulation devices and the like that are easy to deploy, reliably and controllably secured to target tissue and readily removed from target tissue if necessary. What has also been needed is electrical leads that may be used to provide multiple tissue contact points for electrical stimulation signal delivery upon deployment.